The present invention relates to polyphase electrical generators having armature windings connected in various configurations to provide desired output voltage levels. In one embodiment, the present invention relates to a method and apparatus for providing a fine voltage adjustment for the fixed output voltage of a polyphase electric generator for utility and industrial applications.
Conventional utility and industrial electric power generators produce voltages normally between 10.5 kilovolts (kV) to 28 kV. The voltage levels produced by these generators are stepped up by transformers to transmission line voltage levels, typically 40 kV to 400 kV. High voltage generators that directly generate voltages at transmission line voltage levels are becoming increasingly common. These high voltage level generators avoid the need for the step-up transformers and other power distribution components normally associated with converting the lower voltages generated by conventional generators to transmission line voltage levels.
As high voltage generators become more common, the need for step-up transformers may become less and there may be power generation sites at which the step-up transformers are not readily available. However, the same power generation sites employing increasing numbers of high voltage generators often continue to operate conventional low voltage generators. Accordingly, there is a need for a technique for modifying low voltage generators to generate electric power at high voltage transmission line levels.
There is a further need for utility generators that produce electric power at various fixed voltages. Each utility power facility must produce electric power at one or more fixed voltage levels to suit the power transmission line requirements for that power system. These voltage levels are dictated by the requirements of the electric transmission utility and the customary voltages used in the country of the utility. In the United States, typical transmission line voltage levels are 230 kV, 345 kV and 765 kV. Several other countries tend to set transmission line voltages at 400 kV. In Japan transmission line voltages are as high as 1,000 kV. Each power utility will produce electric power at the one transmission line voltage level (and in certain sites at multiple levels) for use in the power distribution grid to which the utility is connected.
Electric generating systems produce power that is at or can be converted to the voltage level required at a particular power utility site. Utility power generation systems are extremely large industrial products that are usually sold worldwide. It is desirable that power generation systems be convertible to match power generation requirements, such as transmission line voltage levels, for various utility and industrial sites throughout the world. In particular, it is desirable that power generation systems, in the United States, be configured to match transmission line voltages of 230 kV, 345 kV and/or 765 kV, and configured in other countries to match the transmission line voltage levels used in those countries.
Generators have historically not been designed to produce electric power at the specific voltage levels of the various power line transmission level requirements. Step-up transformers converted the output voltage levels of generators to transmission line voltage levels. Because of step-up transformers, the generators were not required to produce a variety of output voltages corresponding to the voltage level requirements of each electric power utility distribution grid. The generator need only produce a fixed voltage. Standard voltages for conventional (low voltage) generators are 13.8 kV or 18 kV. These voltages are too low to be applied to power transmission lines. The output voltage of the generator was converted by transformers to transmission line voltage levels.
The voltages produced by the conventional low voltage generators were increased through the use of generator step-up transformers (GSU) to match the generated voltage to the power transmission line voltages. The manufacturers have adapted GSU transformers to match any given generator voltage rating and power transmission line voltage requirements. Accordingly, it has been the responsibility of the transformer manufacturers to provide the necessary selection of fixed voltage levels when connecting generators to particular applications, specifically transmission lines.
Aggressive marketing of high voltage generators has threaten to substantially reduce and possibly eliminate the need for the generator set-up transformers (GSUs). Without GSUs the generators must produce the various fixed output voltages needed to match the various requirements of transmission lines and other generator applications. Accordingly, there is a need for generators having output voltage levels that can be converted to match the various fixed voltage level requirements of electric power transmission lines and other generator applications.
Traditionally, when faced with new generator output voltage requirements, generator manufacturers have redesigned the electromagnetic and mechanical portions of the generator. For example, the manufacturers redesigned the number of winding turns in the armature coils, changed the coils themselves and/or changed the number of stator slots in the generator. A generator redesign would typically involve modifications to the entire character of the machine, including the electrical and mechanical design features. Redesigning generators in this manner is an expensive, long-term and economically-risky program. Designing new generators and redesigning existing generators to match each of the different transmission voltage level requirements would be extremely expensive, burdensome and time-consuming for generator manufacturers.
There is a need for generators that can be easily configured for various fixed voltage output requirements, without having to redesign the entire electrical and mechanical nature of the generator machine. Such generators would allow a manufacturer to make a few standard generator models, and configure each individual generator to a particular customer""s requirements without having to substantially redesign the generator. The economies offered by reducing the variety of generator models offered by an individual manufacturer are tremendous. These advantages include reduced engineering time in designing generators, reduced manufacturing time by having fewer production lines, minimizing spare parts manufacturer, and minimizing need for maintaining and training surface personnel on a large variety of generators.
It is well-known to connect the armature windings of a generator in a Delta or Wye topologies to provide a limited selection of fixed voltage outputs. A conventional Delta topology configuration is shown in FIG. 2 and a conventional Wye topology configuration is shown in FIGS. 3 and 4. These winding topologies allow a generator to operate at a few discrete voltage levels. For example, a three-phase generator may produce voltages at a 100% phase winding voltage level in a Delta configuration and at a 173% phase winding voltage level when in a Wye configuration.
Delta and Wye topologies may each be combined with parallel and series winding arrangements as is shown in FIGS. 5 and 6 to produce voltage level steps of 100% (Delta), 173% (Wye), 200% (Delta), 300% (Delta), 346% (Wye), and so on. These voltage level steps are still separated by relatively large differences. The conventional Delta and Wye configurations did not allow for the selection of voltages that are not at one of these voltage level steps. Conventional Delta, Wye and Delta-Wye combination winding topologies do not allow for fine generator output voltage selections. Thus, a difficulty with these known armature topologies is that they do not allow fine voltage selection and are limited to varying the voltage in certain large steps.
The large voltage steps provided by the Delta and Wye topologies do not allow a generator to be configured to meet an output voltage level requirements that does not correspond to the levels offered by traditional Delta and Wye topologies. There is a need for a fine adjustment of the voltage level output for a utility or industrial generators. A fine adjustment of voltage levels would allow generators to be configured to match a wide variety of voltage level requirements, such as the levels matching transmission lines.
A synchronous generator has been developed having fine adjustment of its voltage level output. The generator may be configured to produce a selected output voltage level at substantially any voltage level within a wide range of available voltages. The voltage level for the generator is set by the arrangement of connections of the end turns of the armature windings of the generator. Once the connections of the armature windings have been set, the generator produces a fixed generated phase voltage that remains constant.
The fine voltage adjustment is provided through a variety of connections between the winding turns of the armature of the generator. These connections between the armature windings are relatively easy to configure because they are essentially external to the main components of the generator, and do not require internal reconfiguration of the generator. By properly connecting the winding turns of the armature, substantially any desired output voltage level can be obtained from the generator within a certain range of available voltages. The ability to select any output voltage level by establishing connections of armature winding turns provides an economical technique for customizing utility and industrial generators for specific voltage level requirements.
The current configurable generator enables a manufacturer to produce a standard generator having uniform arrangements of stator cores, slots, windings and other electromagnetic components. This standard generator is configurable to produce a fixed output voltage from a wide range of available voltages. Because of the technique of configuring connections between windings, substantially any voltage within the range can be selected. This technique provides for fine, incremental steps of voltages along the range of available voltages to be selected by a generator customer. Accordingly, a generator manufacturer may customize each generator to suit a particular customer""s requirement for an output voltage level. The manufacturer may adapt each generator to suit the customer voltage requirement by configuring the interconnections between the winding turns. The manufacturer is spared the expense of having to substantially redesign or reconfigure the internal operating components of the generator.